1. Field of the Invention
The invention relates generally to cooling techniques, and more particularly to techniques for cooling dies in integrated circuit packages.
2. Background
Integrated circuit (IC) dies are typically mounted in or on a package that is attached to a printed circuit board (PCB). Many types of IC packages exist, including leadless chip carriers (LCC), ball grid array (BGA) packages, quad flat packages (QFP), etc. One example advanced type of package is a wafer-level package. Different types of wafer-level packages exist, including wafer level chip scale packages (WLCSP), wafer level ball grid array (WLBGA) packages, and further types. Wafer level packages typically have an array of interconnects located on a bottom external surface of the package die, which may have the form of pads, posts, or balls/bumps (in the case of WLBGA packages). In a WLBGA package, an array of solder bump interconnects may be mounted directly to the die when the die has not yet been singulated from its fabrication wafer. As such, WLBGA packages do not include a package substrate. WLBGA packages can therefore be made very small, with high pin out, relative to other IC package types including traditional BGA packages.
IC packages often are subjected to high temperatures resulting from heat dissipation by circuitry during normal operation. These high temperatures can impair the performance of the circuits and/or cause thermal stresses in the package. Accordingly, a package sometimes includes one or more passive cooling devices, such as heat sinks, coupled to the IC die to facilitate conduction of heat away from the die. However, the mere introduction of passive cooling devices may not adequately dissipate heat from the IC die. Other techniques that are prevalent in industry use active system cooling devices, such as fans. However, in handheld devices and limited-space applications, it typically is not possible to incorporate system level cooling fans. A failure to adequately dissipate heat from the IC die may negatively affect the performance and/or reliability of the IC die.